I'm not nearly done with the game yet, but I can already provide an in-the-works review.
The main words to keep in mind while playing Rayman: Origins are speed and fun. This is a platformer where you're not intended to stop - it runs much more on reflex and fast movement than careful consideration before each action. This may not sound like a good thing, but the controls are so perfectly done that it avoids frustration, and its comprehensive use of classic and recent platforming standards (jumping, wall-running, gliding and much more) makes controlling Rayman instantly familiar.
The first five worlds are designed to each exploit one of Rayman's movements, as a training mode of sorts - but after that, each level becomes a smorgasbord of challenging jumps and climbs and combat, which helps keep the action diversified. Better still, every few levels you will face different activities like special treasure levels where you must chase an escaping chest through quickly collapsing scenery (which is really demanding of your "twitch" platforming skills) and shmup levels where you ride a mosquito and face hordes of enemies all over the screen. There's still multiplayer, which is all kinds of crazy, so much so that words can't do it justice.
The objective of each level is to free Electoons (small round ponytail-wearing characters) from their cages. Each group of Electoons you free adds up to open the next levels, and there are usually hidden cages you can find to open more levels faster. Besides this, the game is littered with Lums, small golden creatures that can add up to become extra electoons; at the end of each level, the game counts up the number of collectables you picked up and rewards you accordingly, so there's actually a reason to spend your time trying to get that one tough collectable you haven't quite figured out how to get to yet.
A big part of Rayman: Origin's charm, however, comes from the way it looks and sounds. The graphics are awesome, with smooth animations and creative level design and everything looks hand-made. It's a shame that you're usually running and jumping around like a maniac and can't stop to take in the scenery. One awesome world in particular is the desert world, where everything that is not sand and wind is a musical instrument. The music is amazingly addictive and tied into the gameplay - Lums are often disposed in a way that they will play a small leitmotif if you pick them up perfectly, and one power-up in particular plays one of the catchiest jingles I have ever heard.
In short, the final score so far is: Super Mario Bros. Wii on crack.